Recently, researches on hybrid construction machinery, which improves fuel efficiency by storing surplus power of an engine in a battery, and supplying power from the battery to the engine that does not have sufficient power so as to cope with a rapid increase in oil price, are being actively conducted.
A system, which uses the engine and an electric motor as a common power source as described above, and has an electrical energy storage device, refers to a hybrid system. For example, as the hybrid system, there is a hybrid system for heavy equipment, such as a hybrid vehicle, and an excavator.
In the meantime, a general excavator system performs an operation of driving, and turning or travelling or a boom, an arm, and a bucket, which are final loads, by using an engine as a power source through a medium, that is, hydraulic pressure. By contrast, a hybrid excavator system may improve total efficiency of the excavator system by additionally installing two motors and an electric storage device to a general excavator. Main components added to the hybrid excavator system include a motor, an electric storage device, an inverter, and a converter. Here, the electric storage device includes a battery and an ultra-capacitor (UC).
FIG. 1A illustrates a hydraulic excavator system in the related art and FIG. 1B illustrates a hybrid excavator system in the related art.
The hybrid excavator system of FIG. 1B additionally uses an electric motor as a power source, in addition to an engine, so that the hybrid excavator system of FIG. 1B has the same basic configuration as that of the hybrid excavator system of FIG. 1A except for the addition of the configuration related to the driving of the electric motor and storage of electrical energy, that is, an engine auxiliary motor 103, an engine auxiliary motor inverter 130, a rotary motor 104, a rotary motor inverter 140, a DC link capacitor 150, a UC 105 for storing electric energy, and a UC converter 160 for supplying electric energy to the UC 105.
That is, both systems commonly and essentially requires mounting of a starting motor 10 for starting the engine 30 and an alternator 20 for charging a battery 101 for supplying electric energy to an excavator electric system 106.
In the meantime, the hybrid excavator in the related art includes two methods, that is, a converter method (FIG. 2A) using a UC converter as a means for supplying electric energy to a UC for storing electric energy, and a converterless method (FIG. 2B) utilizing an initial charging unit instead of a converter.
FIG. 2A illustrates the converter method and FIG. 2B illustrates the converterless methods.
First, a power supply device 100 of the hybrid excavator system according to the converter method of FIG. 2A includes a Switched-Mode Power Supply (SMPS) 110, a logic control board 120, an engine auxiliary motor inverter 130, a rotary motor inverter 140, a DC link capacitor 150, and a UC converter 160 that is DC-DC converter. Here, the SMPS 110, the logic control board 120, the engine auxiliary motor inverter 130, the rotary motor inverter 140, and the UC converter 160 are connected to a control board battery 101, an excavator electric device 102, an engine auxiliary motor 103, a rotary motor 104, and a UC 105, respectively.
The SMPS 110 is connected to the control board battery 101 to supply power to the logic control board 120.
The logic control board 120 performs a function of sensing a voltage of the UC 105 and a voltage of the DC link capacitor 150 and controlling an initial driving logic.
The engine auxiliary motor inverter 130 performs a function of charging the DC link capacitor 150 by the engine auxiliary motor 103. Here, the engine auxiliary motor 103 is directly connected to the engine 30, and rotates at the same rpm as that of the engine 30 when the engine is driven.
When a power connector of the UC 105 is in an on state, the rotary motor inverter 140 performs a function of driving the rotary motor 104 according to a charged voltage. Here, the rotary motor 104 generates power necessary for a rotary operation of an excavator.
The DC link capacitor 150 charges a DC voltage converted by the engine auxiliary motor inverter 130. The DC link capacitor 150 is connected to the UC converter 160.
The UC converter 160 performs a function of charging the UC 105 by using electric energy stored in the DC link capacitor 150. The UC converter 160 is connected between the DC link capacitor 150 and the UC 105. Here, the UC 105 is charged with the voltage converted by the UC 105.
The power converting device 100 including the DC-DC converter including the aforementioned configuration includes an inverter (for example, the engine auxiliary motor inverter 130 and the rotary motor inverter 140) driving a motor and a converter (for example, the UC converter 160) driving the UC. Here, the UC converter 160 accompanies an operation loss during a process of converting a voltage of a DC link to be charged in the UC 105.
However, the UC converter 160 exists, so that there occurs a problem in that an operation loss is generated during the process of converting the voltage of the DC link to be charged in the UC 105, a size of the power converting device 100 is increased, and excessive cost is generated, and in order to solve the problem, a converterless power conversion device, in which the UC converter 160 is omitted, as illustrated in FIG. 2B has been suggested.
Referring to FIG. 2B, the converterless power conversion device has the same configuration as that of the converter method of FIG. 2A, but is different from the converter method of FIG. 2A in that the UC converter 160 is omitted, but an initial charging unit 260 is provided between a DC link capacitor 250 and a UC 105 to charge the UC 105. Further, a small capacity relay (SR1 and SR2) 270 for initial charging and a large capacity connector (MC1 and MC2) 280 for conducting a high current are provided in order to make a voltage of the UC 105 correspond to a voltage of the DC link capacitor 250, so that the UC 105 makes a voltage of the UC 105 correspond to a voltage of the DC link capacitor 250 according to the operations of the small capacity relay (SR1 and SR2) 270 for initial charging and the large capacity connector (MC1 and MC2) 280 for conducting a high current controlled by an initial charging controller 220. The converterless method solves the problem (cost, size, and the like) caused by the existence of the converter.
However, both the converter method of FIG. 2A and the converterless method of FIG. 2B commonly have a problem in that it is necessary to mount a starting motor for starting an engine and an alternator for charging a battery (see FIG. 1B). That is, there are problems in that the starting motor is high-priced, charging/discharging of the battery is repeated through the alternator to cause energy loss, a high current is output to the battery during starting, so that a lifespan of the battery is decreased, and engine efficiency deteriorates due to existence of the alternator, so that it is necessary to solve the problems.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.